Among steel materials, carbon steels for machine construction are inexpensive, and therefore are frequently used in component milling and for mold bases.
When such carbon steels are milled using a typical square end mill that is capable of planar milling and side-surface milling, an example of the end mill being disclosed in patent document 1, a tip corner part which is a portion at which a bottom blade and an outer peripheral blade of a blade part are connected becomes damaged, whereby gouges and deep cuts are produced in a planar milled surface.
Additionally, work material adheres to the cutting blade of each of the blades, such that the same defects as described above are produced due to “built up edge” when the milling operation is performed. Specifically, overcutting of the milled surface due to the development of built up edge formed on the cutting blade, gouges in the milled surface due to built up edge dulling the cutting blade, damage to the milled surface and advanced damage to the tool due to meshing with built up edge that has broken off, and other such defects are produced.
Because all of the defects described above cause deep cuts to be left behind in the milled surface, it is highly labor-intensive to remove these deep cuts when the milled surface is polished. Additionally, the polishing treatment is often performed manually; depending on the technical skill, proficiency, and the like of a worker, the possibility of degradation in milling dimension accuracy may increase. Therefore, it is difficult to obtain a smooth and glossy surface.
In order to overcome such problems, typically, the temperature near the milling point is raised by using an oil-based cutting fluid in an extreme-pressure additive, raising the milling speed, or increasing the amount of incisions, whereby the work material is softened, minimizing damage to the tip corner part of the tool as well as the occurrence of built up edge.
However, it is typically impossible to avoid initiating milling from a normal-temperature state, and when air cutting is incorporated into a milling program, the tool and the work material may be cooled; therefore, in reality, the problems described above are not overcome by the technique described above.